Manufacture of tetraethyllead



nvmvron's GEORGE -w. assn-z women m. TANNER yHYNIIN SHAPIRO G. w. BESTE ErAL' MANUFACTURE OF TETRAETHYLLEAD Filed Dec.

ALLOY C omposl'non-welsu-n'v lnczufiaumuwl .40 20 Sept. 22, 1953 5 a wa AVE .6 LC w 3 p K f w n we 1 a Ac Y o L A A e T .P A N C B III I'" w m m F' 0 so ALLOY COMPOSITION'WEIGHTPER CENT LEAD Patented Sept. 22, 1953 MANUFACTURE OF TETRAETHYLLEAD George W. Beste and Homer M. Tanner, Baton Rouge, La., and Hymin Shapiro, Detroit, Mich., assignors to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application December 24, 1949, Serial No. 135,002

6 Claims.

This invention relates to the manufacture of tetraethyllead. More particularly, the invention relates to a process for the manufacture of tetraethyllead from a lead-sodium alloy whereby greatly increased conversion of the lead to tetraethyllead is obtained.

Tetraethyllead in the past has been made by the reaction of ethyl chloride with an alloy of 10 percent sodium and 90 percent lead. The reaction is carried out under pressure and at an elevated temperature of 75 to 90 C. in an autoclave wherein the reactants are stirred or agitated. Upon completion of the reaction, excess or unreacted ethyl chloride is vented off, and the reaction products are discharged into water in a still. The tetraethyllead is then separated by steam distilling from the other reaction prodpcts.

While this process has been commercially successful, it has several marked disadvantages. A principal disadvantage is the low conversion of lead to the desired tetraethyllead product. Despite repeated and lengthy efforts to improve the lead conversion,the best result obtained is a conversion of 21 to 22.5 percent of the lead to tetraethyllead. Hence approximately threefourths of the lead charged is unreacted and mustbe recovered by expensive drying and smelting operations. The large amount of unreacted lead in the reaction products is disadvantageous because it increases the difiiculty of separation or recovery of the tetraethyllead product. The excess or unreacted lead has an additional adverse effect in that it operates as an inert or inactive portion of the autoclave charge. Therefore, the reaction equipment is not fully utilized because a substantial portion of the reaction space is taken up by non-reacted lead.

The prime object of our invention is to provide a process accomplishing a substantially greater conversion of lead to tetraethyllead. A further object is to reduce the amount of unreacted metallic lead which must be recovered by smelting operations. An additional object is to increase the proportion of reactive material in the reaction vessel, that is, to increase the portion of the lead charged which is capable of conversion to tetraethyllead.

We accomplish these objects by reacting an alloy of lead and sodium, containing from 79 to 86.5 weight percent lead, with ethyl chloride in the presence of a yield-increasing catalyst such as ethyl acetate. It has been discovered that our process provides a greatly increased conversion of the lead to tetraethyllead, as much as 60 percent more being obtained by our method than is realized from the same amount of lead when processed by the conventional method using an alloy containing percent lead. The particular benefits of the process will be more readily understood in connection with the accompanying figure. The figure, which is explained in more detail hereafter, shows the typical increases in lead conversion attainable with lead-sodium alloys within the scopeof and by our process.

In general, our process is carried out by introducing a charge of comminuted alloy into the reaction vessel. Ethyl chloride, in excess of the quantity theoretically required to convert all the lead to tetraethyllead, is then added. The catalyst is usually added simultaneously with and in solution in the ethyl chloride. The charge is then agitated or stirred and heated to reaction temperature. The agitation is continued throughout the reaction to thoroughly contact the solid alloy and the ethyl chloride. On completion of the reaction, the excess or unreacted ethyl chloride is vented and the charge is cooled to moderate temperatures. The reacted mixture is then discharged to a still vessel and the tetraethvllead is separated by steam distillation.

The use of a catalyst is essential to our process, and we have found many materials which are satisfactory yield increasing catalysts. Ketones, aldehydes, and the esters of carboxylic acids are, in particular, very effective catalysts. In addition, there are numerous other catalysts not included in these groups, which are also highly effective. The following compounds are examples of catalysts of lthe ester type which are suitable for our process: ethyl formate, butyl acetate, amyl acetate, benzyl butyrate, ethyl acetate, ethyl isobutyrate, ethyl butyrate, ethyl benzoate, ethyl n-caprylate, ethylalpha-hydroxy isobutyrate, ethyl isovalerate, ethyl n-valerate, ethyl isoamyl caproate, and para cresyl benzoate.

As examples of aldehydes which are effective as catalysts in the process of our invention are n-amyl einnamaldehyde, anisaldehyde, acrolein, butyraldehyde, 2-ethyl butyraldehyde, n-heptaldehyde. phenyl acetaldehyde, paraiso'oropvl benzaldehyde, sodium sulfobenzaldehyde, tiglaldehyde, 2-ethyl-2-hexenal, benzaldehyde and acetaldehyde.

Ketones are very effectve catalysts, especially the lower molecular weight compounds. The following are examples of eflicient catalystsin this group: acetone, acetophenone, benzal acetophenone, mesityl oxide, methyl-ethyl ketone, phorone, tertiary butyl-methyl ketone, methylisobutyl ketone, and benzophenone.

- As already mentioned there are other eflective catalysts not included in the foregoing list of examples. Among these specific catalysts are n-heptyl alcohol, tertiary butyl alcohol, isobutyl alcohol, secondary =butyl alcohol, cetyl alcohol, octyl alcohol, triethyl amine, alpha picoline, gamma-picoline, diphenyl carbamine chloride, and morpholine.

The following example illustrates a typical method or carrying out our process, as well as illustrating typical benefits obtained thereby. All quantities or proportions given herein are in terms parts by weight or weight percentages.

Example one hundred parts by weight 01' a lead-sodium alloy containing 80.3 percent lead was introduced as a comminuted solid into a reaction vessel, and 138 parts of ethyl chloride and 0.5 part of acetone were then introduced. The reaction vessel was then closed and heated to 100 C. for 3 hours. On completion of the reaction, 46 parts of tetraethyllead were recovered from the reaction mass, corresponding to a conversion of 37 percent oi. the lead to tetraethyllead. In contrast, when the sam procedure is followed except that no acetone or any other catalyst is used, only 5 parts of tetraethyllead are recovered, corresponding to a conversion of 4.1 percent of the lead.

As previously stated, the process is applicable when producing tetraethyllead from sodium-lead alloys containing from 79 percent to 86.5 percent lead. A yield or conversion increase is obtained throughout this range, but all the alloys are not fully equivalent. In fact, we have found that the greatest lead yield or conversion is obtained using an alloy containing 80 weight percent lead. Further, the surprising discovery was made that in addition to being the most eflicient alloy composition for the process, an 80 percent lead alloy is a limiting or critical composition. It alloys oi. slightly less lead content are used, the conversion to tetraethyllead decreases very greatly, to substantially no conversion at all at a composition of 79 weight percent lead. The alloy composition containing 80 percent lead is therefore not only the optimum composition with respect to obtaining greatest lead'conversion, but is also critical in that an alloy containing only one percent less lead is practically non-eflective for producing tetraethyllead.

We have further found that the range of alloy compositions, from 80 to 81.8 weight percent lead is significant in that the greatest conversion increases are obtained within this range.

The importance and efiect or the alloy composition in the process will be more easily understood by reterence to the accompanying figure. The figure illustrates the variation in conversion and the conversion improvement obtained in ethylating sodium-lead alloys of varying composition. Referring to the figure, two plots are given showing the conversion of lead to tetraethyllead. The curves GE and EF' are a plot of the conversion of lead to tetraethyllead obtained by carrying out the ethylation reaction according to our process. The curve GBC shows, for direct contrast, the results obtained when sodium-lead alloys of the same composition are contacted with ethyl chloride at reaction conditions, but without using any of the yield increasing catalysts of our process. The curve AG shows the conversion 01' lead obtained over a limited range of alloy compositions, from the limit G of our process to the alloy composition A employed in the convention commercial operation.

The curves of the figure are based on a series oi ethylation experiments carried out at 100 C. Ethyl chloride was used in excess of the quantity theoretically required to convert all the lead in the alloy, and the reaction was carried out according to the procedure in the preceding example. A catalytic amount of acetone was used in the catalyzed series of reactions. Point A shows the results obtained using the alloy of the present commercial operation which contains 90 percent lead. A conversion eillciency of 21.6

the lead conversion obtained by the catalyzed reaction increases, and at an increasing rate, with a decrease in the lead content of the alloy from 86.5 to 80 percent, as shown by the curve GE. On the other hand, the conversion obtained by the uncatalyzed reaction shows only a slight increase when alloys of less than 86.5 percent lead are used. In fact, if the alloy composition has less than 81.8 percent lead, the conversion in the absence of our catalysts, is then drastically lower.

This is illustrated by the plot GBC, showing that the conversion increases only slightly with a change in lead content from 86.5 to 81.8 percent lead, and that it decreases extremely rapidly with a further decrease in lead content below 81.8 percent lead.

It is apparent from the curves FE and EG, and CBG, that the catalyzed process of our invention provides an improvement in lead conversion throughout the range of alloy compositions from '79 to 86.5 percent lead, that is, an improvement.

over the amount of tetraethyllead obtained over that obtained by the non-catalyzed reaction from alloys of the same composition. The process is doubly beneficial when alloys are used in the range of less than 81.8 down to 80 percent lead.

As heretofore pointed out, when using alloys of this composition, the conversion of lead is greatest, and in addition this is exhibited with alloys which are substantially non-reactive in the absence of catalysts. In other words, in using alloys varying from 81L8 to percent lead, the greatest conversion improvements are obtained by our process, as well as the greatest absolute yields.

The use 01' alloys containing from 79 to 80 weight percent lead is encompassed by the process, since a substantial improvement in conversion is obtained over the non-catalyzed reaction. 01 course, in a portion of this range, the actual yields of tetraethyllead are not favorable, being less than the yield obtained by the conventional process. It is important to note, however, that although the conversion of lead decreases very rapidly for a decrease in leadcontent below 80 weight percent, ctr-specification alloys could still be used and a satisfactory conversion would be obtained. By off-specification alloys, we mean alloys containing a few tenths 01' a percent less lead than required for the highest conversion, for

example, alloys containing 79.8 or 79.9 weight percent lead.

The surprising benefits of our process are fully apparent from the figure as described above. By our process, a conversionof over 36 percent of the lead charged to tetraethyllead is obtainable.

In contrast, the prior commercial process obtains a conversion of only 21.6 percent of the lead. In other words, it is now possible to make over 1600 pounds of tetraethyllead from the same quantity of lead as would produce only 1000 pounds by the previous process.

The alloys for our process are comminuted preferably before use. The comminution is necessary to provide adequate surface for reaction of all the alloy. The particular size distribution of the alloy is not critical. Thus, particles varying from one-half inch to one-sixteenth inch in diameter are entirely suitable; It will be found preferable to avoid very fine dusts, because such extremely small particles require exceptional care in preparation and transport to avoid oxidation. It is customary, of course, to maintain inert atmospheres over sodium-lead alloy during preparation and storage.

Temperature of operation is not a highly critical factor in carrying out our process, that is, it is operable through a. substantial range of temperatures to provide conversion improvements over the conversion ,obtained by an uncatalyzed reaction. However, with respect to the absolute or actual yield obtained, the optimum temperature range is from 100 to 120 0., although good conversions have been obtained from as low as 80 C. to as high as 140 0., above and below the aforementioned preferred temperature range. However, the actual yield decreases outside the preferred range so that it will be highly desirable to operate within 100 to 120 C.

As an illustration of the effect of temperature on our process, we give below the results of a series of ethylations at different temperatures of an alloy containing 81.8 percent lead. Three theories of ethyl chloride were used, based on the lead content. some runs were made with 2.3 weight percent ethyl acetate as catalyst and another series was made at the same. conditions, but in the total absence of a catalyst.

The tabulation following shows the conversion of lead to tetraethyllead when carrying out the catalyzed process at different temperatures. In

addition, the tabulation gives the ratio of the quantity of tetraethyllead produced by the catalyzed reaction to that obtained by the uncat- These results show that the conversions obtained by our process vary only slightly within the preferred range of 100 to 120 C. It will also be noted that the lead conversion realized by our process is consistently substantially greater than obtained by an uncatalyzed reaction. As our process is less sensitive to the eflect of temperature than is an uncatalyzed reaction, the ratio of lead conversion is greatest at the upper and lower limits of the to C. operating range. At these limits, conversions of lead by an uncatalyzed reaction are extremely low, but by our process high conversions are still obtained.

The process is necessarily carried out at an elevated pressure? Pressure is not a critical factor in our operation, however, and need be only great enough to maintain the ethyl chlo ride reactant in the liquid phase. The operating pressure is thus substantially identical with the vapor pressure of ethyl chloride. The operating pressures will thus vary from 100 to about 360 pounds per square inch, the pressures for the preferred temperature range being 160 to 250 pounds per square inch.

As stated heretofore. we utilize an excess of ethyl chloride over and above that theoretically required to react with all the lead charged. The preferred quantity of ethyl chloride is from to 400 parts by weight per 100 parts of lead. These proportions are preferred because of operating or practical advantages rather than because of a pronounced effect on the conversion of lead to tetraethyllead. There are several reasons why an excess of ethyl chloride is desirable. The liquid ethyl chloride acts as a relatively efficient heat transfer medium from providing a uniform temperature throughout the reaction charge. Further, the excess ethyl chloride insures that all of the particles of alloy ,are uniformly contacted with ethyl chloride, so that g the degree of reaction is substantially the same throughout the reacting mixture. An excess of unreacted ethyl chloride is also desirable at the termination of the reaction, as the vaporization and venting of the excess ethyl chloride facilitates removal of heat from the reacted material.

As already described, numerous catalysts have been found effective in our process. The reasons for catalytic yield increasing effectiveness are not fully understood. In general, it has been found that the effective catalysts most frequently contain a group or radical such as the CO group in ketones, the CO0 group in esters, and the CH0 group such as in aldehydes. Organic compounds which are similar structurally, but do not contain such an effective group, are in general, ineffective for our purpose. Thus, hydrocarbons or hydrocarbon halides are not effective as catalysts.

Carboxylic acids or acid anhydrides are to be avoided, as they are detrimental. Likewise, organic peroxides are detrimental. Other compounds which are detrimental to the reaction are the nitroalkanes, amides, nitriles and cyclic nitrogen compounds.

The catalysts may be used over a fairly wide range of concentration and will be effective throughout this range. In general, the necessary catalyst proportion is equivalent to 0.5 percent of the lead charged or above. Concentrations above 0.5 percent do not provide any substantial further increase in yield. In some instances, the minimum catalytic amount required will be slightly greater than 0.5 percent, particularly for the catalysts of higher molecular weight. The usual preferred amount of catalyst used is from 1 to 3 percentbased on the lead in the alloy charged. v

The preferred mode of catalyst addition is to dissolve it in the ethyl chloride to be fed. This method assures that all particles of the alloy will be'exposed to the catalyst simultaneously with the contact with the ethyl chloride. This type of addition is not vital, however. If desired, the catalyst can be added separately after the ethyl chloride has been introduced. The catalyst should not be added prior to the addition of ethyl chloride.

The process is carried out under anhydrous conditions, as it has been found that any substantial amount of free water strongly depresses the yields obtainable. As an example of the adverse eifect of water, when 100 parts of alloy containing 80 percent lead is reacted by our process, a conversion to 45 parts of tetraethyllead is obtained. The addition of 39 parts of water to the reaction vessel so strongly depressed the conversion that less than 9 parts of tetraethyllead were recovered. This illustrates the adverse efl'ects of free water which should be carefully avoided in the process in contrast to some of the methods heretofore described in the literature' The presence of minute traces ofwater, such as' would be found in commercial supplies of catalysts, is not objectionable.

The mixture of reaction products from the process includes the tetraethyllead product, excess lead and sodium, sodium chloride formed by combination of the sodium fed with chlorine from the reacted ethyl chloride, and excess ethyl chloride. The latter is customarily vented off to a recovery system, leaving an apparently dry mass of powdered solids which is usually referred to as reaction mass. The tetraethyllead is ordinarily recovered from reaction mass by steam distillation, but other methods can also be used.

It will be evident from the foregoing description of the process that the objects thereof are fully accomplished. It will also be apparent that many variations of the process are possible without departing from the scope thereof, as defined in the following claims.

We claim:

1. The process for the manufacture of tetraethyllead comprising reacting under anhydrous conditions at a temperature of from 80 to 140 C. an alloy consisting essentially of sodium and lead containing from 80 to 86.5 weight percent lead, with ethyl chloride in the presence of a lead ethylation catalyst.

2. The process forthe manufacture of tetraethyllead comprising reacting under anhydrous conditions at a temperature of from 100 to 120 C. an alloy consisting essentially of sodium and lead containing from to 86.5 weight percent lead, with ethyl chloride in the presence of a lead ethylation catalyst.

3. The process for manufacture of tetraethyllead comprising reacting under anhydrous conditions at a temperature of from 80 to 140 C. an alloy consisting essentially of sodium and lead, containing from 80 to 81.8 weight percent lead, with ethyl chloride in the presence of a lead ethylation catalyst.

4. The process for manufacture of tetraethyllead comprising reacting under anhydrous conditions at a temperature of to C. an alloy consisting essentially of sodium and lead, containing from 80 to 81.8 weight percent lead. with ethyl chloride in the presence of a lead ethylation catalyst.

5. The process for the manufacture of tetraethyllead comprising reacting under anhydrous conditions at a temperature of from 80 to C. an alloy consisting essentially of sodium and lead, containing from 80 to 81.8 weight percent lead, with ethyl chloride in the presence of a catalytic amount of acetone.

6. The process for the'manufacture of tetraethyllead comprising reacting under anhydrous conditions at a temperature of 100 to 120 C., 100 parts by weight of lead in an alloy consisting essentially of sodium and lead and containing from 80 to 81.8 weight percent lead, with from to 400 parts by weight of ethyl chloride and in the presence of from 1 to 3 parts by weight of acetone.

GEORGE W. BESI'E. HOMER M. TANNER. HYMIN SHAPIRO.

References Cited in the file of this patent UNITED STATES PATENTS Number 

1. THE PROCESS FOR THE MANUFACTURE OF TETRAETHYLLEAD COMPRISING REACTING UNDER ANHYDROUS CONDITIONS AT A TEMPERATURE OF FROM 80 TO 140* C. AN ALLOY CONSISTING ESSENTIALLY OF SODIUM AND LEAD CONTAINING FROM 80 TO 86.5 WEIGHT PERCENT LEAD, WITH ETHYL CHLORIDE IN THE PRESENCE OF A LEAD ETHYLATION CATALYST. 